1. Field of the Invention
The present invention relates to an electrophotographic machine, and, more particularly, to a method and apparatus for minimizing visual artifacts in images resulting from laser scan processing.
2. Description of the Related Art
In an in-line color electrophotographic imaging process, latent images are formed on a plurality of photosensitive drums, which are in turn developed using a predetermined color of toner. The developed images are transferred to an intermediate transfer device or directly to a sheet of media, such as paper, which travels past the photosensitive drums. Each color image is created one line at a time and the lines are oriented at right angles to the direction of travel of the intermediate transfer device or the paper. The individually generated images on each drum are combined on the paper to form a single full-color image. In a typical multi-color laser printer, for example, the sheet of paper passes through four color-developing stations in series, with the colors being black, magenta, cyan and yellow.
It is recognized that in order for the multi-color laser printer to accurately print an image, the laser beam, or beams, for each of the four colors must be in alignment, both in the scan direction (across the page) and in the process direction (feed direction of the paper). Providing proper alignment of the laser printheads relative to the sheet of media in each direction can be difficult. This problem is compounded with the addition of each printhead, since the plurality of printheads must be in registration so that the individual images generated by each printhead can be correctly superimposed when they are combined.
In order to reduce the cost of a laser printer a single scanning polygon mirror may be utilized to reflect the laser beams from multiple laser sources. Laser beams are directed through an optical system that includes lenses and mirrors. The optical path taken by the laser beams are offset in a single polygon mirror system. As such, as the laser light passes through some of the optics there can be a bending or bowing of the light as it travels across its scan.
What is needed in the art is a method and apparatus for minimizing artifacts and images resulting from laser scan process directional errors, such as printhead skew and laser beam bow.